This invention relates to compositions which are suitable for refrigeration applications and to the use of such compositions in heat transfer devices such as refrigeration and air conditioning systems. The invention relates, in particular, to refrigerant compositions which can be used in the applications currently satisfied by trichlorofluoromethane (refrigerant R-11).
Heat transfer devices of the mechanical compression type such as refrigerators, freezers, heat pumps and air conditioning systems are well known. In such devices a refrigerant liquid of a suitable boiling point evaporates at low pressure taking heat from a neighbouring heat transfer fluid. The resulting vapour is then compressed and passes to a condenser where it condenses and gives off heat to another heat transfer fluid. The condensate is then returned through an expansion valve to the evaporator so completing the cycle. The mechanical energy required for compressing the vapour and pumping the liquid may be provided by an electric motor or an internal combustion engine.
In addition to having a suitable boiling point and a high latent heat of vaporisation, the properties preferred of a refrigerant include low toxicity, non-flammability, non-corrosivity, high stability and freedom from objectionable odour.
Hitherto, heat transfer devices have tended to use fully and partially halogenated chlorofluorocarbon refrigerants such as bromotrifluoromethane (refrigerant R-13B1), trichlorofluoromethane (refrigerant R-11), dichlorodifluoromethane (refrigerant R-12), chlorodifluoromethane (refrigerant R-22) and the azeotropic mixture of chlorodifluoromethane and chloropentafluoroethane (refrigerant R-115); the azeotrope being refrigerant R-502. Refrigerant R-11, for example, has been widely used in chillers.
However, the fully halogenated chlorofluorocarbons in particular have been implicated in the destruction of the earth""s protective ozone layer and as a result the use and production thereof has been limited by international agreement.
Whilst heat transfer devices of the type to which the present invention relates are essentially closed systems, loss of refrigerant to the atmosphere can occur due to leakage during operation of the equipment or during maintenance procedures. It is important, therefore, to replace fully halogenated chlorofluorocarbon refrigerants by materials having low or zero ozone depletion potentials.
In addition to the possibility of ozone depletion, it has been suggested that significant concentrations of chlorofluorocarbon refrigerants in the atmosphere might contribute to global warming (the so-called greenhouse effect). It is desirable, therefore, to use refrigerants which have relatively short atmospheric lifetimes as a result of their ability to react with other atmospheric constituents such as hydroxyl radicals.
Replacements for some of the chlorofluorocarbon refrigerants presently in use have already been developed. These replacement refrigerants tend to comprise selected hydrofluoroalkanes, i.e. compounds which contain only carbon, hydrogen and fluorine atoms in their structure. Thus, refrigerant R-12 is generally being replaced by 1,1,1,2-tetrafluoroethane (R-134a).
Although suitable replacement refrigerants are available, there is always a need for new refrigerants having a low or zero ozone depletion potential that are capable of replacing the chlorofluorocarbon refrigerants presently in use such as R-11. Furthermore, very real benefits could be realised by a new replacement refrigerant having a higher refrigeration capacity than the chlorofluorocarbon refrigerant it is replacing.
The present invention provides a composition comprising a mixture of compounds having zero ozone depletion potentials which can be used, for example, in chillers as a replacement for refrigerant R-11. The composition of the invention can exhibit an advantageously high refrigeration capacity.
According to the present invention there is provided a composition comprising:
(A) 1,1,2,2,3-pentafluoropropane (CF2HCF2CFH2); and
(B) at least one hydrofluorocarbon selected from the group consisting of 1,1,1,3,3-pentafluoropropane (CF3CH2CF2H) and 1,1,1,2,2,3,3,4,4-nonafluorobutane (CF3CF2CF2CF2H).
The present invention also provides a heat transfer device, such as a chiller, comprising an evaporator, a condenser, a compressor and an expansion valve in which there is contained a refrigerant composition comprising:
(A) 1,1,2,2,3-pentafluoropropane (CF2HCF2CFH2); and
(B) at least one hydrofluorocarbon selected from the group consisting of 1,1,1,3,3-pentafluoropropane (CF3CH2CF2H) and 1,1,1,2,2,3,3,4,4-nonafluorobutane (CF3CF2CF2CF2H).
The composition of the invention comprises (A) 1,1,2,2,3-pentafluoropropane (R-245ca) which has a boiling point of about 25xc2x0 C. and (B) at least one hydrofluorocarbon selected from 1,1,1,3,3-pentafluoropropane (R-245fa) and 1,1,1,2,2,3,3,4,4-nonafluorobutane (R-329ccb), both of which have a boiling point of about 15xc2x0 C. Although component (B) may comprise a mixture of R-245fa and R-329ccb, it will preferably comprise just one of these compounds and more preferably will comprise just R-329ccb.
The composition of the invention tends to boil and condense over a fairly narrow temperature range and, as a result, tends to exhibit fairly small temperature glides in both the evaporator and condenser. Furthermore, the composition tends not to fractionate (separate) into its constituent components to any significant degree on boiling so that the liquid and vapour phases that will be present in the refrigeration cycle will tend to have similar compositions. The terms azeotrope and azeotropic are well known of course and refer to compositions comprising two or more components which exhibit constant boiling behaviour and which do not fractionate into their constituent components upon boiling or evaporation. Thus, the composition of the invention exhibits properties which are not too far removed from that of a true azeotrope and in this regard may be termed azeotrope-like or near-azeotropic.
The amounts of the R-245ca and of the at least one hydrofluorocarbon selected from R-245fa and R-329ccb in the composition of the invention may be varied within wide limits, but typically the composition will comprise from 10 to 90% by weight of R-245ca and from 10 to 90% by weight of at least one hydrofluorocarbon selected from R-245fa and R-329ccb.
When component (B) is R-245fa, a preferred composition of the invention in terms of its suitability as a replacement for refrigerant R-11 is one comprising from 15 to 85% by weight of R-245ca and from 15 to 85% by weight of R-245fa.
When component (B) is R-245fa, a particularly preferred composition of the invention in terms of its suitability as a replacement for refrigerant R-11 is one comprising from 20 to 30% by weight, more particularly about 25% by weight, of R-245ca and from 70 to 80% by weight, more particularly about 75% by weight, of R-245fa.
When component (B) is R-245fa, another particularly preferred composition of the invention in terms of its suitability as a replacement for refrigerant R-11 is one comprising from 45 to 55% by weight, more particularly about 50% by weight, of R-245ca and from 45 to 55% by weight, more particularly about 50% by weight, of R-245fa.
When component (B) is R-245fa, a further particularly preferred composition of the invention in terms of its suitability as a replacement for refrigerant R-11 is one comprising from 70 to 80% by weight, more particularly about 75% by weight, of R-245ca and from 20 to 30% by weight, more particularly about 25% by weight, of R-245fa.
When component (B) is R-329ccb, a preferred composition of the invention in terms of its suitability as a replacement for refrigerant R-11 is one comprising from 40 to 95% by weight of R-245ca and from 5 to 60% by weight of R-329ccb.
When component (B) is R-329ccb, a particularly preferred composition of the invention in terms of its suitability as a replacement for refrigerant R-11 is one comprising from 40 to 80% by weight, more particularly from 70 to 80% by weight, of R-245ca and from 20 to 60% by weight, more particularly from 20 to 30% by weight, of R-329ccb. An especially preferred composition of the invention in terms of its suitability as a replacement for refrigerant R-11 is one comprising about 75% by weight of R-245ca and about 25% by weight of R-329ccb.
The refrigerant composition of the invention may also be combined with one or more hydrocarbons in an amount which is sufficient to allow the composition to transport a mineral oil or alkyl benzene type lubricant around a refrigeration circuit and return it to the compressor. In this way, inexpensive lubricants based on mineral oils or alkyl benzenes may be used to lubricate the compressor.
Suitable hydrocarbons for inclusion in the refrigerant composition of the invention are those containing from 2 to 6 carbon atoms, with hydrocarbons containing from 3 to 5 carbon atoms being preferred. Hydrocarbons that will not significantly alter the refrigerant thermophysical properties at the level at which they provide for oil transport, such as the linear and branched isomers of butane and pentane are particularly preferred, with pentane being especially preferred.
Where a hydrocarbon is included, it will preferably be present in an amount of from 1 to 10% by weight on the total weight of the refrigerant composition.
The refrigerant composition of the invention may also be used in combination with the types of lubricants which have been specially developed for use with hydrofluorocarbon based refrigerants. Such lubricants include those comprising a polyoxyalkylene glycol base oil. Suitable polyoxyalkylene glycols include hydroxyl group initiated polyoxyalkylene glycols, e.g. ethylene and/or propylene oxide oligomers/polymers initiated on mono- or polyhydric alcohols such as methanol, butanol, pentaerythritol and glycerol. Such polyoxyalkylene glycols may also be end-capped with suitable terminal groups such as alkyl, e.g. methyl groups. Another class of lubricants which have been developed for use with hydrofluorocarbon based refrigerants and which may be used in combination with the present refrigerant compositions are those comprising a neopentyl polyol ester base oil derived from the reaction of at least one neopentyl polyol and at least one aliphatic carboxylic acid or an esterifiable derivative thereof. Suitable neopentyl polyols for the formation of the ester base oil include pentaerythritol, polypentaerythritols such as di- and tripentaerythritol, trimethylol alkanes such as trimethylol ethane and trimethylol propane, and neopentyl glycol. The esters may be formed with linear and/or branched aliphatic carboxylic acids, such as linear and/or branched alkanoic acids. Preferred acids are selected from the C5-8, particularly the C5-7, linear alkanoic acids and the C5-10, particularly the C5-9, branched alkanoic acids. A minor proportion of an aliphatic polycarboxylic acid, e.g. an aliphatic dicarboxylic acid, may also be used in the synthesis of the ester in order to increase the viscosity thereof. Usually, the amount of the carboxylic acid(s) which is used in the synthesis will be sufficient to esterify all of the hydroxyl groups contained in the polyol, although residual hydroxyl functionality may be acceptable.
The composition of the present invention may be used to provide the desired cooling in heat transfer devices such as chillers by a method which involves condensing the composition and thereafter evaporating it in a heat exchange relationship with a heat transfer fluid to be cooled. In particular, the composition of the invention may be employed as a replacement for refrigerant R-11 in chillers.
In addition to its use as a refrigerant, the composition of the invention may also be used as an aerosol propellant, as a foam blowing agent for blowing polyolefin, polyurethane and related foams, or as a solvent in degreasing or extraction applications.
The present invention is now illustrated but not limited with reference to the following examples.